Filtering device for a canned motor

ABSTRACT

A canned motor has a housing and a motor shaft which extends through the housing. A rotor is fixed to the shaft and is located in a rotor compartment within the housing. The rotor compartment has a flow path for circulation of a cooling and lubricating fluid through the compartment. A sleeve surrounds the shaft upstream of the flow path and is surrounded by a second sleeve. The two sleeves cooperate to define a gap which serves as a filter for fluid entering the rotor compartment. The minimum height of the gap is smaller than the minimum height of the flow path to prevent suspended solid particles which can obstruct the flow path from entering the latter. The sleeves are composed of a hard material so that oversized particles can be ground down by causing the fluid to repeatedly bring the particles into contact with the sleeves.

BACKGROUND OF THE INVENTION

The invention relates to a filtering device for a canned motor.

Various designs and various filter inserts for such filtering devicesare known - e.g., from the British patent application 1 237 633. Theyare used mainly in canned motor pumps which function to conveycontaminated fluids. The known filtering devices are mostly situated inthe wall between the pressure chamber of the centrifugal pump and therotor chamber of the canned motor. The filter insert, which consists ofa porous material, a strainer or the like, tends to become clogged aftera period of time which depends upon the type and quantity of the solidinclusions. This leads to interruption of the rinsing stream conductedthrough the rotor chamber so that the heat generated in the canned motordue to power losses is no longer adequately removed. As a result of thiscircumstance, continuous monitoring and frequent maintenance(replacement or cleaning of the filter insert) are necessary.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a filtering device forcanned motors which, on the one hand, traps solid particles having asize such that the downstream gap is endangered and, on the other hand,is not imperiled by obstruction or clogging.

According to the invention, the object set forth is achieved in that afiltering gap bounded by sleeves of hard material is established betweenthe housing and the rotor shaft and has a minimum width smaller than theminimum width of the downstream gap situated in the path of the rinsingstream inside the rotor chamber.

The principle of the invention is to allow small (harmless) particles topass but to hold back larger inclusions until they have been ground to asafe size by the walls of the sleeves which define the filtering gap.

In accordance with the invention, the filtering gap can be constructedso as to enhance the grinding action of the filtering gap and increasethe life of the sleeves forming the filtering gap.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail with reference thedrawings in which:

FIG. 1 is a section through a canned motor in the area of the filteringdevice; and

FIG. 2 is a section showing the motor of FIG. 1 coupled to a centrifugalpump.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a canned motor 11 has a rotor shaft 2 which isdisposed in a housing 1. A ceramic sleeve 3 is inserted in the housing 1and surrounds a sleeve 4 which has been pushed onto the rotor shaft 2and likewise consists of ceramic. The confronting walls of the sleeves3, 4 bound a filtering gap 5 located upstream of the rotor chamber 6 ofthe canned motor.

As shown in FIG. 2, a channel 7 in the housing 1 serves for theintroduction of rinsing fluid from the pressure chamber 13 of acentrifugal pump 12. The channel 7 has an axially extending portionopening into a plurality of bores 8 which extend radially in the sleeve3 and are distributed over the periphery thereof. The bores 8, in turn,open into an annular compartment 9 likewise defined by the sleeve 3. Theannular compartment 9 narrows in the direction of the filtering gap 5situated before the rotor chamber 6.

A passage 10 extending axially through the shaft 2 is provided fordischarge of the rinsing fluid from the rotor chamber 6 as best seen inFIG. 2. The rinsing fluid arriving at the annular compartment 9 via thechannel 7 and the bores 8 contains solid particles having a size greaterthan the width of the filtering gap 5. These particles are initiallyretained in the ring of fluid circulating upstream of the filtering gap5. The current directed towards the rotor chamber again and againentrains a portion of the solid particles and conveys them to the inletof the filtering gap 5. The particles are there gradually ground untilthey finally enter the filtering gap 5. Since they are here alsosubjected to a grinding action, their size at the end of the filteringgap is such that the following gap is no longer endangered. They are nowcarried along by the rinsing fluid, conducted through the rotor chamber6 and withdrawn via the passage 10.

I claim:
 1. A canned motor, comprising a housing defining a rotorcompartment and a first gap for the flow of a fluid through saidcompartment, said first gap having a first width; a rotor shaftextending through and defining with said housing a chamber upstream ofsaid first gap; and filtering means provided in said chamber andincluding a rotary first tubular element which surround said shaft and astationary second tubular element which surrounds said first tubularelement, said tubular elements together defining a second gap having asecond width less than said first width, said tubular elements togetherconstituting a grinding means for suspended solids entering said secondgap so that solids too large to pass through said second gap are groundprior to entering said first gap.
 2. The motor of claim 1, wherein eachof said tubular elements comprises a hard material.
 3. The motor ofclaim 2, wherein at least one of said tubular elements comprises aceramic.
 4. The motor of claim 1, wherein said tubular elements haverespective surface portions which face one another, at least one of saidsurface portions being rough.
 5. The motor of claim 1, wherein saidsecond gap is arranged so that fluid flows towards said second gap inthe axial direction of said shaft.
 6. The motor of claim 1, wherein saidsecond gap narrows in a direction towards said compartment.
 7. The motorof claim 1, wherein said second gap has an inlet and said tubularelements together define an annular compartment in the region of saidinlet.
 8. The motor of claim 7, wherein said second gap is annular andhas an outer diameter, said annular compartment having a diametergreater than said outer diameter.
 9. A canned motor, comprising ahousing defining a rotor compartment and a first gap for circulation ofa fluid through said compartment, said first gap having a first width; arotor shaft extending through and defining with said housing a chamberupstream of said first gap; and filtering means in said chamber, saidfiltering means including a rotary first tubular element which surroundssaid shaft and a stationary second tubular element which surrounds saidfirst tubular element, said tubular elements together defining a secondgap having a second width less than said first width, said second gapbeing arranged so that fluid flows toward said second gap transverselyof said shaft.
 10. The motor of claim 9, wherein said second gap has aninlet and said second tubular element is provided with at least oneradial opening in the region of said inlet.